Add passthrough GP for cases where no color or coverage should be emitted by GP

src/gpu/GrGeometryProcessor.h

Index: src/gpu/GrGeometryProcessor.h
diff --git a/src/gpu/GrGeometryProcessor.h b/src/gpu/GrGeometryProcessor.h
index 4d041d64bc91be14cadf53deebe326f62d48a5b4..49fcdaf4b009556e4fb28413e3c1d33703c742e9 100644
--- a/src/gpu/GrGeometryProcessor.h
+++ b/src/gpu/GrGeometryProcessor.h
@@ -19,6 +19,13 @@
  */
 class GrGeometryProcessor : public GrPrimitiveProcessor {
 public:
+    /**
+     * Creates a simple geometry processor that reads device-space positions as the first vertex
+     *  attribute (vec1, offset=0) and passes it through. It does no color or coverage calculation

[egdaniel, 2015/10/14 21:22:13]

extra space at start of comment?

+     *  and assumes no coord transforms are required by any FPs.
+     */
+    static const GrGeometryProcessor* CreatePassthroughGP(size_t vertexStride);
+
     GrGeometryProcessor()
         : INHERITED(false)
         , fWillUseGeoShader(false)